A. Field of the Invention
The present invention relates to an improved method for preparing a trans fat free all purpose shortening composition.
B. Background Art
Shortening is the common term for semi-solid fats used in food preparation, especially baked goods. The material make-up of shortening has changed over time, from a natural fat (e.g., butter, lard) to blends of oils with hard fats to hydrogenated liquid oils to blends of oils with additives like emulsifiers, antioxidants, anti-foamers, metal scavengers, anti-spattering agents, etc. Shortenings can be found in virtually every type of prepared food product, and affect the structure, stability, flavor, storage quality, eating characteristics, and eye appeal of such products. Two approaches are widely practiced to develop a desired solid fat content profile for the specific temperatures required in food preparation applications: hydrogenation of a source oil and/or the addition of solid fats to a source oil.
The introduction of hydrogenation (circa 1910) to the development of vegetable shortenings enabled the production of shortenings with increased oxidative stability, improved uniformity and enhanced performance characteristics. Additionally, the improvement of processes for solidification, filling, packaging and crystallization were devised to enhance the appearance and performance of shortenings. As a result, pure vegetable shortening with increased stability and improved creaming properties (typically, bland, white in color, and featuring a smooth texture) were accepted by both consumers and industrial users or bakers.
Hydrogenation of an unsaturated fatty acid refers to the addition of hydrogen atoms to the acid, causing double bonds to become single ones as carbon atoms acquire new hydrogen partners (to maintain four bonds per carbon atom). Full hydrogenation results in a molecule containing the maximum amount of hydrogen (in other words, the conversion of an unsaturated fatty acid into a saturated one). Partial hydrogenation results in the addition of hydrogen atoms at some of the empty positions, with a corresponding reduction in the number of double bonds. In most naturally occurring unsaturated fatty acids, the hydrogen atoms are on the same side of the double bonds of the carbon chain (cis isomers). However, partial hydrogenation reconfigures some of the double bonds that do not become chemically saturated, twisting them such that the hydrogen atoms end up on different sides of the chain (trans isomer). The trans isomer formation is lower in energy, and favored in the hydrogenation process.
Commercial hydrogenation is typically partially accomplished in order to obtain a malleable fat that is solid at room temperature, but melts upon baking (or consumption). Partially hydrogenated vegetable oils are also available in a wide range of consistencies and have other desirable characteristics (i.e., longer shelf life), making them the predominant ingredient in pure vegetable shortenings, today. Pure vegetable shortenings are made from refined edible vegetable oils, usually a blend of two or more partially hydrogenated oils.
Each source oil exhibits inherent crystallization tendencies, passing through one or more unstable crystalline stages before assuming either a β or β′. β crystals are large, coarse and self-occluding. β′ crystals are small and needlelike, tending to pack together into dense, fine-grained structures. Edible oil products contain various combinations of β and β′ tending components, and the ratio of a β-β′ contributes to the dominant crystal habit. Typical conventional shortening compositions comprise a major oil source that tends to form a β crystals, combined with a minor oil source that tends to form β ′ crystals. The minor oil source then serves to promote β′ crystals for improved plasticity.
Pure commercially available vegetable shortenings may currently be made by blending 8 to 10% of a hard fat to promote β′ crystallization (typically palm or cottonseed oil fully hydrogenated to an iodine value of roughly 1-8) with a soybean oil shortening base, consisting of soybean oil hydrogenated to an iodine value of about 75 at roughly 425° F. and 10 psi. This mixture is pumped into a small closed system, where the fat is continuously solidified through a scraped surface heat exchanger. The fluid mixture is supercooled to about 80 to 85° F., wherein small β crystals begin to form. The supercooled mixture is then pumped into a worker unit to continue the growth of small crystals without additional cooling. The resulting shortening composition is packed and allowed to temper at about 80° F. for 1 to 3 days to achieve the required crystal structure. In this process, crystallization of the shortening may be achieved with some level of inaccuracy.
During the last decade or more, consumers have become increasingly interested in the quantity of trans isomers (also known as “trans fats”) present in food products. Before 2006, consumers in the United States could not directly determine the quantity of trans fats in prepared food products. Indeed, the presence of trans fats could only be inferred from the ingredient list, notably from identifying any partially hydrogenated ingredients. On Jul. 11, 2003, the Food and Drug Administration (FDA) issued a regulation requiring manufacturers to list on the Nutrition Facts panel the amount of trans fats of prepared food products and some dietary supplements. The labeling rule required mandatory compliance by Jan. 1, 2006 (although companies could petition for an extension to Jan. 1, 2008). The regulation allows trans fats in levels of less than 0.5 grams per serving to be labeled as “zero grams per serving.” The FDA did not approve nutrient content claims such as “trans fat free” or “low trans fat,” because it opted to not establish a Recommended Daily Value. However, the FDA defines “trans fat” as a fat containing one or more trans isomers not in a conjugated system. This is an important distinction, as it distinguishes non-conjugated synthetic trans fats from naturally occurring fatty acids with conjugated trans double bonds, such as conjugated linoleic acid.
The FDA estimates that by 2009 trans fat labeling will have prevented from 600 to 1,200 cases of coronary heart disease and 250 to 500 deaths each year. This benefit is expected to result from consumers choosing alternative foods lower in trans fats, as well as manufacturers reducing the amount of trans fats in their products.
Cities across the United States are acting to reduce consumption of trans fats. In May 2005, Tiburon, Calif., became the first American city where all restaurants voluntarily cook with trans fat free oils. Montgomery County, Md., approved a ban on partially hydrogenated oils, becoming the first county in the nation to restrict trans fats. New York City barred restaurants from using most frying and spreading fats containing artificial trans fats above 0.5 grams per serving by Jul. 1, 2007, and in all of their foods by Jul. 1, 2008. By Sep. 1, 2007, eateries in Philadelphia must cease frying food in trans fats, and by Sep. 1, 2008, trans fat cannot be used as an ingredient in Philadelphia commercial kitchens (excluding small local bakeries).
In an effort to reduce the quantity of trans fats in prepared food products, including shortenings, manufacturers have turned to alternative processes for producing shortenings and other prepared food products. One alternative is the introduction of higher levels of saturated fats, which naturally contain higher solid fat contents. Some typically used saturated fats include palm oil, palm kernel oil, and coconut oil. However, diets high in saturated fats contribute to heart disease. Replacing trans fats with saturated fats is not an acceptable alternative for shortening manufacturers.
Emulsification provides yet another alternative to preparing shortening compositions with desirable physical characteristics. The introduction of emulsified shortenings (circa 1933) enabled the development of specialty shortenings designed for specific applications. For example, shortenings containing mono- and diglyceride emulsions, in addition to the source oils, exhibited a finer dispersion of smaller sized fat particles, thus strengthening cakes and permitting higher sugar levels. Super-glycerinated shortenings produced moister, higher volume cakes, and, remarkably, lighter icings with higher moisture levels. Presently, specialty shortenings have been designed for applications as diverse as layer cakes, pound cakes, cake mixes, cream fillings, icings, whipped toppings, breads, sweet dough, puff pastries and other baked products. Although mono- and diglyceride emulsifiers are created from saturated fats, their introduction into shortening compositions does not impart a significant increase in the amount of saturated fats compared to conventional shortening compositions, and imparts a significantly lower amount of saturated fats compared to shortening compositions low in trans fats due to the replacement of partially hydrogenated vegetable oils with higher solid fat content oils such as palm or coconut.
Recently, a mono- and diglyceride emulsifier having an elevated concentration of diglycerides was discovered to achieve desirable shortening characteristics, when suspended in a liquid source oil, without the introduction of harmful trans fats and without a significant increase in additional saturated fats compared to conventional all purpose shortenings. In particular, mono- and diglyceride emulsifiers with an elevated level of diglycerides have been shown to promote a β crystalline formation upon recrystallization after melting. Therefore, the development of emulsifiers with elevated levels of diglycerides holds great potential for the development of useful trans fat free prepared food products. Moreover, diglycerides demonstrate much weaker interaction with water, and can be used at much higher levels in many applications with little or no reformulation. Diglycerides also recrystallize from a melt more quickly than triglycerides with similar fatty acid profiles. As a result, various blends of diglycerides may be used to mimic or improve the melting behavior of common fat-based products, and eliminate the need for minor source oils to promote a β′ crystal growth, these source oils typically having higher levels of hydrogenation and/or saturated fats.
One problem, however, is that crystallization of an emulsified shortening using high diglyceride emulsifiers cannot be accomplished using the known manufacturing process for preparing shortenings from partially hydrogenated oils. In practice, traditional partially hydrogenated soybean oil shortening may be manufactured on a continuous line system at speeds of approximately 28,000 pounds per hour. Mono- and diglyceride emulsifiers crystallize rapidly over a smaller range of temperatures. Therefore, in order to successfully manufacture trans fat free shortenings manufactured from blends containing non-hydrogenated vegetable oils with mono- and diglyceride emulsifiers, the manufacturer must more precisely control crystallization in the product line, as well as the amount of work applied to the blend to form the shortening composition, by reducing the speed within the line system, and by controlling the cooling rate within the scraped surface heat exchanger. Embodiments of the present invention address the problem of manufacturing a trans fat free shortening using emulsifiers, particularly mono- and diglyceride emulsifiers with an elevated level of diglycerides, and provide methods for manufacturing shortening compositions that contain essentially zero grams of trans fats per serving and that do not contain significantly increased levels of saturated fats.